Thames water levels

[534l4rk]

Although the E.A. have been keeping levels under better control over the last 8 years it does appear that with the forecast heavy rain that the present levels are still high over much of the Thames. Would it not be better to lower levels before the rain arrives ?

 

[teddington_lock]

Locks work to target levels , you can't just drop the level by a foot here and there to 'make room' for the rain , or you get boats on the bottom , houseboats breaking service pipes , abstraction problems , giant holes and peaks coming downriver to name just a few.

I would imagine most locks are within their target levels at the moment.

Don't let the tailwater of the lock deceive you , it's the headwater level you need to watch.

River levels are monitored by river control 24/7 , when a high (or low) level alarm goes off , then the river duty officer is informed and he can act accordingly. In the daytime , the lock keepers tend to act before the alarm levels are reached , but out of hours , the duty officer will call out lock staff as needed once river control have been in touch.

 

[boatone]

River management requires that each stretch is kept within certain limits (nominally -3" to +6" ) in each stretch if at all possible. Lots of reasons including keeping boats afloat, extraction etc but main management is needed when flow is high and opening weirs helps up to point where all fully drawn and nothing else to do until flows start to subside again.
Doubt that deliberately lowering levels before water arrives would help much and would probably cause other problems.
Have you noticed how quickly a level falls or drops within an hour or less of a weir movement? I woke up aground at Sonning earlier this year and within half an hour of closing in the weir we were afloat again.

 

[534l4rk]

Thank you for your responses TL and Boatone. However my query relates not to particular stretches but to the whole length. If the levels over the whole length were lowered to the levels approaching those frequently reached during the summer months months when we have little rain - would this not lessen the chances of river flooding ? This would only relate to times when there is definite heavy rain forecast.

 

[stuartbaggs]

I'm sure the EA have it covered. As TL said you can't just lower river levels without a negative impact elsewhere.

 

[No Regrets]

Problem is, if you lowered the River, and things got a bit dry, there would be a premature shortage of water. It would make no difference to flow either, should it rain a lot!!

Optimal level is correct!

 

[david_bagshaw]

Although the E.A. have been keeping levels under better control over the last 8 years it does appear that with the forecast heavy rain that the present levels are still high over much of the Thames. Would it not be better to lower levels before the rain arrives ?

Interestingly the Dutch lower the level of the ijsselmeer and the levels of the fixed mastroute between Amsterdam and Gouda in the winter by 0.07 mtr.

 

[alanch]

The EA, in the past, have closed the Thames barrier at Woolwich at low water to prevent the flood tide passing further upstream. This leaves an empty river from Woolwich to Teddington to fill up with flood water rushing downstream. After the high tide, when the two level out, they open the Barrier and it all ebbs away. Works a treat, but it severely screws up the self scouring effect the river normally has below the barrier and the PLA have to fork out for dredging.

 

[534l4rk]

My original posting acknowledged the improved control of the Thames by the E.A. over the last 8 years. Checking further it would appear that we have had the highest rainfall in November since 2000 (Natural Environment Research Council). My layman analysis of river level data from the monitor stations still suggests that reducing the levels before forecast rain would lessen the probabilities of flooding.

 

[boatone]

My layman analysis of river level data from the monitor staions still suggests that reducing the levels before forecast rain would lessen the probabilities of flooding.

Whilst I can see where you are coming from, at the very best it would only result in flooding being delayed for a few hours and there would be many undesirable side effects. In terms of our particular interest in boating, many boats would be left aground during the reduced levels period with the possibility of damage to underwater gear.
In many stretches, the maintained depth for navigation is barely achieved as it is.

 

[Chris_d]

My original posting acknowledged the improved control of the Thames by the E.A. over the last 8 years. Checking further it would appear that we have had the highest rainfall in November since 2000 (Natural Environment Research Council). My layman analysis of river level data from the monitor staions still suggests that reducing the levels before forecast rain would lessen the probabilities of flooding.

I think reducing levels would only delay flooding by a few hours, once the weirs are all wide open the river will only hold so much water, it has to go somehwere. There is nothing the EA can do at the monent except wait for the water to go away

 

[534l4rk]

Based on how long it takes for water up river to effect the lower non tidal reaches it appears to me to take days not hours. Irrespective, navigation is not recommended under fast flow conditions. Surely, the increased levels give more problem to moored vessels than lower levels ?

 

[534l4rk]

Doesn't the time it has taken to reduce levels over the whole Thames justify my original query ?

 

[Riverleak]

Don't just think about the navigation! If you try to reduce river levels in advance of flooding you upset the whole Eco system. Losing fish stock, aquatic life in all it's diversity, plants, birds, etc, as well as the possibility of abstracting water for human consumption. With the small amount, realitively speaking, the river could hold without flow, it's an inconceivable option. I hope that give you another angle of thought...

 

[534l4rk]

The levels I was talking about are those frequently reached during Summer months over the years.

 

[Riverleak]

Providing there is not heavy rain, I believe the lock staff maintain the river levels the same all the year through 24/7 365, if it's possible, the -3 +6 headwater levels apply all the year through, and as I understand it, are not just laid out entirely for purposes of navigation.

 

[534l4rk]

Providing there is not heavy rain, I believe the lock staff maintain the river levels the same all the year through 24/7 365, if it's possible, the -3 +6 headwater levels apply all the year through, and as I understand it, are not just laid out entirely for purposes of navigation.

But I oriiginally only queried when there was a definite forecast for heavy rain. I have no doubt that the levels maintained under other circumstances are realistic.